1. Field of the Invention
The present invention relates to a supporting frame structure for a tension-type shadow mask of a color CRT and particularly, to a supporting frame structure for a tension-type shadow mask of a color CRT, wherein the curvature of the supporting frame for a tension-type shadow mask supporting frame for a color CRT having upper and lower tensions in a form of a single curvature, changes to have a form of a poly-nomial after compression is added.
2. Description of the Background Art
FIG. 1 is a sectional view showing the conventional color CRT.
A front surface glass referred to as a panel 1, and a rear surface glass referred to as a funnel 2, are combined together. Inside the glasses is a fluorescent screen 4, an electron gun (not shown) which is a source of the electron beam 6 for hitting the fluorescent screen 4, a shadow mask 3 for selecting color to radiate a predetermined fluorescent material, and a frame 7 for supporting the shadow mask 3.
In addition, a spring 8 for combining the frame 7 to the panel 1 and an inner shield 9 for shielding so that the color CRT is influenced less by the external geomagnetism during the operation of the color CRT are fixed on the frame 7 in high-degree vacuum.
In the operation of the color CRT, the electron beam 6 hits the fluorescent screen 4 formed on the inner surface of the panel 1 by a bipolar voltage applied to the color CRT in the electron gun (not shown) built in the neck of the funnel 2. At this time, the electron beam 6 is deflected toward the upper, lower, left and right directions by a deflection yoke 5 before reaching the fluorescent screen 4, to thus form a screen.
Also, the frame 7 has a magnet with poles 2, 4 and 6 for adjusting the orbit of the electron beam 6 so that the electron beam 6 hits a certain fluorescent material pixel in the fluorescent screen 4 precisely.
The color CRT is under high-degree vacuum and accordingly breakage is occurs easily. Therefore, to prevent the breakage of the color CTR, the panel 1 is designed to have strength enough to endure atmospheric pressure. Also, the color CRT is provided with a reinforcing band 11 formed in the skirt portion of the panel 1, and accordingly, the color CRT is constructed to have a sufficient impact resistance by dispersing stress applied to the color CRT under high-degree vacuum.
FIGS. 2A and 2B are a perspective view showing a supporting frame structure for a shadow mask according to a conventional art and a structure of curvature of a main frame before compression on the main frame, respectively.
FIGS. 3A and 3B are a perspective view showing a supporting frame structure for a shadow mask according to a conventional art and a structure of curvature of a main frame after compression on the main frame, respectively.
As shown in FIG. 2A, a shadow mask assembly for a color CRT having upper and lower tensions comprises upper and lower main frames 11 for supporting the shadow mask, and a sub frame 12 which functions as an elastic suspending member and to which elastic force is applied in case of assembling the shadow mask by compressing the main frame 11 for fixing and supporting the main frame 11.
As shown in FIG. 2B, before compression is performed in the main frame 11 by forming a single curvature when the main frame 11 is compressed in order to prevent the shadow mask wrapping, the curvature of the main frame 11 conventionally has the form of poly-nomial.
As shown in FIGS. 3A and 3B, the radius of curvature of the main frame 11 after the compression in the main frame 11 can be identically formed to have a single curvature in every position, by forming a radius of curvature at the center of the main frame 11 smaller than that of curvature in a peripheral portion on both sides of the main frame 11 before the compression on the main frame 11.
Namely, as shown in FIG. 2B, when the size of a radius of curvature at the central portion in the main frame 11 is R1 and the size of a radius of curvature at the peripheral portion in the main frame 11 is R2, the structure of a radius of curvature satisfies the relation R1<R2.
FIGS. 4A, 4B and 4C are schematic views and graphs showing compression load and displacement according to a conventional art, and FIG. 5 is a detailed view showing a radius of curvature and curvature structure of a supporting frame structure for a shadow mask before and after frame compression according to conventional art.
As shown in FIGS. 4A, 4B and 5 compression load T is applied to the peripheral portions at the right and left sides more than 2 times greater than at the center when the main frame 11 is compressed and the shadow mask is assembled.
However, at the peripheral portions of the main frame 11, there is a sub frame 12 to which elastic force is applied and accordingly, the compression displacement δ is greater than 2 times at a center portion of the main frame 11 than at the peripheral portion.
Accordingly, to form the after-compression radius of curvature of the main frame 11 as a single curvature, the size of the after-compression radius of curvature of the main frame 11 at the central portion is smaller than that at the peripheral portion.
Namely, in case that the compression load at the center portion of the main frame 11 is T1, compression displacement at the center portion is δ 1, the compression loads at the left and right peripheral portions of the main frame 11 are T2 and compression displacements at the right and left peripheral portions of the main frame are δ 2, the relations T1<T2 and δ 1>δ 2 are satisfied.
FIG. 6 is a perspective view showing a structure combined with a general damper wires according to a conventional art.
As shown in FIG. 6, to improve howling characteristics generated by the vibration of a shadow mask at left and right peripheral portions, after compression and welding the shadow mask on a main frame 11, one to three damper wires 13 for reducing the vibration of the shadow mask 3 are attached to the shadow mask 3 in the horizontal direction (X direction) in the structure of the shadow mask assembly for a color CRT having upper and lower tensions.
The damper wires 13 are fixed to damper springs 14 having a certain tension and the damper springs are attached on side portions of the sub frame 12.
According to the howling characteristics, howling phenomenon is not recognizable since the center portion of the shadow mask 3 vibrates in Z direction and a screen change on which fluorescent material spreads and a landing change are not distinguishable.
However, at left and right peripheral portions of the shadow mask 3, the change in landing causes the howling phenomenon even though the shadow mask 3 vibrates a little and accordingly, damper wires 13 are attached to reduce the vibration of the shadow mask 3.
FIG. 7 is a schematic view showing elastic force of the conventional damper wire.
However, in a supporting frame structure for a conventional tension-type shadow mask of a color CRT, as shown in FIG. 7, in case that the aftercompression radius of curvature of the frame is formed in a structure of a single curvature, a problem of howling phenomenon occurs since compression force t1 on the shadow mask 3 is stronger at the center portion than t2 at the peripheral portions of the shadow mask 3. Also, in case of increasing the tension of the damper wires to improve the howling characteristics, the damper wires are easily broken because the thickness of the damper wires is as thin as 20˜30 μm.